The invention relates to a method for establishing the position of an actuating unit which is operated by an electric motor. The invention also relates to brakes, pumps and transmissions in which actuating units of this kind are used.
In the case of, for example, an electronic parking brake (EPB) which is operated by an actuating unit the motor speed is as a rule currently measured by sensor technology (for instance by means of a Hall sensor). The number of detected revolutions (or of pulses delivered by the Hall sensor) multiplied by a motor constant gives the travel completed by the actuating unit. However high costs are incurred by fitting a Hall or another sensor.
Approaches for establishing a motor speed without a sensor, e.g. from the number of commutation changes, are already known. However these have the disadvantage of being susceptible to faults. The patent DE 197 29 238 C1, and corresponding U.S. Pat. No. 6,144,179, both of which are incorporated by reference herein, describes, for example, a method for establishing the speed of mechanically commutated D.C. motors in which the speed is established from a motor state model in parallel with the detection of the waviness (current ripple) of the motor current. The speed is firstly established from the motor state model, which is based on the electromechanical motor equations, after which a reliable set time range is predetermined for the following commutating process. If no waviness is detected within this set time range on account of a fault, the probable speed and the probable commutating instant derived from the latter are assumed.
The object of the present invention is to precisely establish the travel of an actuating unit without using additional sensor technology. A further object of the present invention is to enable the travel of the actuating unit to be quickly determined continuously or at short time intervals.